A couple things, MyVoice. Please do not use text messaging on this site. Second, this site is designed to share information for all, and we delete individual email addresses, which is why I edited your post.
I also deleted Subhash's replay; Subhash, please stop posting rude replies to requests for information or I will request you be banned. One of your links went to an entirely unrelated website and your link to FAQs did not address MyVoice's question, which is relatively specific in comparison with many requests we've received here.
MyVoice, if you're preparing a whitepaper on migration testing, you'll need to consider that the testing requirements differ depending on both the technology and the nature of the data to be migrated.
For example, I may be migrating a given db to a new schema. I may be changing code bases (similar to your example).
One relatively "common" consideration is that snapshot of data is performed before the migration, and compared after the migration. There is often a complete regression test, to ensure functionality is still operational and/or that the migrated data is still accessible and usable.
Special attention must be given to backing up and retaining old data, in case of major failure; some shops will test the backout procedure if the information/systems are critical.
Others will have significant input, I'm sure, but it's a big topic and dependent on exactly what is being migrated...